The present disclosure relates to a solid-state imaging element, a manufacturing method, and an electronic device, and particularly to a solid-state imaging element, a manufacturing method, and an electronic device that can improve image quality more.
In related art, solid-state imaging elements such as CMOS (Complementary Metal Oxide Semiconductor) image sensors, CCD (Charge Coupled Device) image sensors, and the like are widely used in digital still cameras, digital video cameras, and the like. A solid-state imaging element has a light receiving surface in which a plurality of pixels having a PD (photodiode) as a photoelectric conversion section, a plurality of transistors, and the like are arranged two-dimensionally. Each of the pixels subjects incident light to photoelectric conversion.
For example, in a CMOS image sensor, a charge accumulated by photoelectric conversion in a PD is transferred to an FD (Floating Diffusion) as a floating diffusion region via a transfer transistor. Then, the charge accumulated in the FD is converted into a pixel signal corresponding to the level of the charge by an amplifying transistor, and the pixel signal is output via a selecting transistor.
In general, a saturation charge amount by which a charge can be accumulated in the PD is determined by parameters such as the area (that is, a physical area and depth) of the PD, the potential depth of the PD, an electric field between a surface pinning layer formed on the surface of the PD and the PD, and the like.
The area of the PD is determined by the size of the pixel (cell size), a plurality of transistors possessed by the pixel, a pixel separating section for separating the pixel, and the like. In addition, the physical depth of the PD and the potential depth of the PD are determined by ease of readout of a charge from the PD to the FD. In addition, an electric field between the PD and the surface pinning layer forms a PN junction capacitance, and an accumulable charge can be increased according to the intensity of the electric field even with a same potential difference. However, the electric field of too high intensity becomes a source of a leakage. Thus, the electric field is determined by a tradeoff in relation to the occurrence of the leakage.
The saturation charge amount of the PD is thus determined by a plurality of factors. However, it is difficult to simply increase the saturation charge amount because of limitations in terms of characteristics.
Japanese Patent Laid-Open No. 2010-16114 (referred to as Patent Document 1 hereinafter) discloses for example a technology that intensifies an electric field at a side wall of a PD by forming a PN junction capacitance on the side of a trench element isolation region, and which technology thereby increases the saturation charge amount of the PD.